Pass the correct webState to the nativeContent.

If an offline content is created in a new tab, currentWebState in the
BVC will return the webState from the original tab (created tab is in
background).

Pass the webState from the webController instead.

BUG=685969

Review-Url: https://codereview.chromium.org/2655463014
Cr-Commit-Position: refs/heads/master@{#446753}
7 files changed